1. Technical Field
The present invention relates to a hard phase forming alloy powder that may preferably be used for forming a hard phase dispersed in a wear resistant sintered alloy. The wear resistant sintered alloy, such as that used in valve sheets for internal-combustion engines, must have wear resistance at high temperatures. The present invention also relates to a production method for a wear resistant sintered alloy using the hard phase forming alloy powder, and the wear resistant sintered alloy may preferably be used for valve sheets for internal-combustion engines. In addition, the present invention relates to a wear resistant sintered alloy obtained by the production method.
2. Background Art
For a sintered alloy, the alloy design can be freely selected, and various characteristics, such as heat resistance and wear resistance, can be easily added thereto compared to doing so for ingot materials. Therefore, the sintered alloy is used for valve sheets for internal-combustion engines. In such wear resistant sintered alloy for valve sheets, a hard phase having a high degree of hardness is generally dispersed in an iron-based alloy matrix primarily to improve wear resistance. For example, the following sintered alloys are known. A sintered alloy, in which ferroalloy particles are dispersed in an iron-based alloy matrix as a hard phase, is disclosed in Japanese Patent Application of Laid-Open No. 64-015349. This sintered alloy is formed by adding a ferroalloy powder, such as ferromolybdenum and ferrotungsten, to a raw powder and then sintering. Another sintered alloy, in which a hard phase is dispersed in an iron-based alloy matrix, is disclosed in Japanese Patent Application of Laid-Open No. 09-195012. This sintered alloy is formed by adding a high-speed tool steel powder or a die steel powder to a raw powder and then sintering, and metal carbides are dispersed in the hard phase. Specifically, when high wear resistance is required for a sintered alloy, it is preferable that a Co-based alloy powder or a Ni-based alloy powder (see Japanese Patent Application of Laid-Open No. 10-046298) be added to a raw powder and be dispersed as a hard phase. For the Co-based alloy powder, a Co—Cr—W alloy (see Japanese Patent Application of Laid-Open No. 64-015349) and a Co—Mo—Si alloy (see Japanese Patent Application of Laid-Open No. 56-152947) may be used.